1. Field of the Invention
The present invention relates to a magnetostatic wave device, and particularly to a magnetostatic wave device which is used in a filter such as a band-pass filter and a band-stop fiIter, a delay line and the like.
2. Description of the Prior Art
FIG. 9 is a perspective view showing an example of the conventional magnetostatic wave device. The magnetostatic wave device 1 comprises a YIG (Yttrium, Iron, Garnet) thin film 2 as a ferrimagnetic base material. The YIG thin film 2 is formed on one main surface of a GGG (Gadolinium, Gallium, Garnet) substrate 3. On the YIG thin film 2, two fine wire conductors 4a and 4b as transducers are disposed in parallel with a space therebetween. Meanwhile, the other main surface of the GGG substrate 3 is bonded to one main surface of a ground conductor 5. One end of the wire conductor 4a and the other end of the other wire conductor 4b are respectively connected to the ground conductor 5.
FIG. 10 is a perspective view showing another example of the conventional magnetostatic wave device. In the magnetostatic wave device 1, a surface of a YIG thin film 2 on a GGG substrate 3 is bonded to one main surface of a dielectric substrate 6. On one main surface of the dielectric substrate 6, two microstrip lines 7a and 7b as transducers are formed in parallel with a space therebetween so as to cross the YIG thin film 2. On the other main surface of the dielectric substrate 6, a ground conductor 5 is formed. Meanwhile, one end of the microstrip line 7a is connected to the ground conductor 5 through one side of the dielectric substrate 6. The other end of the other microstrip line 7b is connected to the ground conductor 5 through the other side of the dielectric substrate 6.
In the magnetostatic wave devices 1 shown in FIG. 9 and FIG. 10, a d.c. magnetic field is applied to the YIG thin film 2, respectively. In these magnetostatic wave devices 1, for example, when a high-frequency signal is inputted to one transducer, a high-frequency magnetic field is generated around the transducer by the high-frequency electric current flowing in the transducer, and a predetermined magnetostatic wave is excited in the YIG thin film 2, respectively. The magnetostatic wave is propagated from one transducer to the other transducer. When the d.c. magnetic field is applied to the YIG thin film 2 in a direction orthogonal to the main surface of the YIG thin film 2, a magnetostatic forward volume wave (MSFVW) is excited. When the d.c. magnetic field is applied in a direction which is parallel to the YIG thin film 2 and perpendicular to the direction of propagation of the magnetostatic wave, a magnetostatic surface wave (MSSW) is excited. When the d.c. magnetic field is applied in a direction which is parallel to the YIG thin film 2 and to the direction of propagation of the magnetostatic wave, a magnetostatic backward volume wave (MSBVW) is excited.
The magnetostatic wave is received by the other transducer and is outputted therefrom as a predetermined high-frequency signal. The magnetostatic wave device 1 is used, for example, in a band-pass filter, a band-stop filter and a delay line.
In the magnetostatic wave devices 1 shown in FIG. 9 and FIG. 10, though a sharp resonance characteristics is obtained, a band width is wide.